Interestingly at TWC's Computer Recycling Linux outsells Windows systems by about 3 to 1 (it was 5 to 1 a few weeks ago). I think the biggest drawing point is the cost. Our Linux machines are a bit less than the Windows machines. Another factor that probably helps is that we run Ubuntu on almost all of our own machines, so when someone comes in they can actually sit down and try it out. We also try to support people when they want a printer, web cam, or some special piece of hardware. I think the number could even be stronger this year as we continue to develop our support system.
When people ask about the cost difference only a small part is the actual licensing costs. Microsoft gives is a pretty incredible deal on licensing (with some caveats, our Windows computers are not available to everyone and we cannot just sell licenses or CDs). Most of the cost comes from the amount of work that has to go into building a Windows computer. Linux used to get slagged for no drivers, but that's actually what our issue with Windows is, we have to do a lot more work to get drivers for Windows on refurbished systems -- Linux usually has most drivers built into the kernel, and on the occasion that we need to get a proprietary driver the hardware drivers under System/Administration usually does the trick.